Inspection device and inspection method

ABSTRACT

An inspection device for inspecting defects of an inspection object including a light source for irradiating a luminous flux to the inspection object; an optical system for guiding reflected light from the inspection object; a photoelectric image sensor having a plurality of photoelectric cells arranged, for converting the light guided to detection signals; a detection signal transfer unit having channels each constituted by a signal correction unit, a converter and an image formation unit, and corresponding to each of a plurality of regions formed by dividing the photoelectric image sensor, respectively; and an image synthesis unit for forming an image of the surface of the object by synthesizing partial images outputted; the inspection device inspecting defects of the object by processing the synthesized image; whereby it becomes possible to correct a detection signal from said photoelectric cell close to a predetermined reference target value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an inspection device for inspecting defectiveimages and adhering foreign matters of an inspection object on whichimages are formed, such as a wafer, a liquid crystal panel, a mask, andso forth, and an inspection method for this inspection device.

2. Description of the Related Art

In a semiconductor production process, for example, foreign mattersexisting on a semiconductor substrate or pattern defects created duringthe production process cause defects such as inferior insulation andshort-circuit and lower a production yield. Smaller foreign matters ordefects, if any, may result in a critical problem with furtherminiaturization of semiconductor devices and more delicate defectdetection becomes therefore necessary.

The defects and the foreign matters are detected in an early stage of aproduction process by using a semiconductor inspection device on asemiconductor production line, for example, and the causes of thedefects are specified and are fed back to the production process so asto improve the production yield.

However, an equivalent inspection sensitivity cannot always be obtainedby an inspection device of the same type and even when the sameinspection object is inspected, differences often occur in the numberand kind of defects detected.

To reduce the inspection sensitivity difference (machine difference)among the inspection devices (machines), it is import to conductadjustment of the inspection sensitivity and to keep conformity but itis practically difficult to render the inspection sensitivity of theinspection devices (machines) uniform owing to variance of performancesof elements that constitute the inspection device (machine). Therefore,a correction method for reducing the variance has been required.

JP-A-2005-201782 as one of the prior art technologies of this kinddiscloses a technology for reducing noise resulting from a detectionsystem by combining a plurality of sensors and correcting signals.

JP-A-2003-346698 describes a method for correcting influences offluctuation resulting from non-uniformity of electron beam dosage andtime by using a plurality of detectors in an electron beam apparatus andindividually executing gain correction and offset correction for each ofthe detectors.

The reference described above, i.e. JP-A-2003-346698, describes also amethod for correcting non-uniformity of signal intensity inside a visualfield by dividing a two-dimensional sensor into a plurality of regionsand correcting a digital level of an output signal for each of theregions divided.

Another reference JP-A-4-362790 discloses a method for correcting lightpower fluctuation by an exposure time in a scan type sensor.

Still another reference JP-A-2006-250739 describes illumination lightcorrection in an illumination optical system by changing a shape of areflecting surface to execute aberration correction.

SUMMARY OF THE INVENTION

The prior art technologies described above can adjust the inspectionsensitivity or the image formation sensitivity by making uniform thelevels of the individual detection signals of each inspection device(machine), it is true, but do not take into consideration how to keepconformity of the inspection sensitivity among the respective inspectiondevices (machines).

When a light source the illumination intensity distribution of which isnot uniform inside an inspection visual field but which has a plane-likedistribution is used, a noise level will increase when a detectionsignal of an inspection region having different illumination intensityis deliberately increased and the inspection sensitivity cannot bealways improved.

It is therefore an object of the invention to provide an inspectiondevice that can reduce an inspection device (machine) difference ofoutput signals from a photoelectric image sensor owing to variance ofoptical performance of each inspection device (machine) and can keepconformity of inspection sensitivity, and an inspection method for theinspection device.

It is another object of the invention to reduce a machine difference ofinspection sensitivity among a plurality of inspection devices(machines) resulting from variance of performances of constituentelements such as an illumination system having a light source, anoptical system for guiding reflected and scattered light, a detectionsystem having a photoelectric image sensor, and so forth, by correctingdetection signals from the detection system.

According to one aspect of the invention, there is provided aninspection device for inspecting defects or foreign matters on a surfaceof an inspection object, including a light source for irradiating aluminous flux to the inspection object; an optical system for guidingreflected and scattered light reflected from the inspection object; aphotoelectric image sensor having a plurality of photoelectric cellsarranged, for converting the reflected and scattered light guided toelectric detection signals; a detection signal transfer unit havingchannels each constituted by a signal correction unit, an A/D converterand an image formation unit, and corresponding to each of a plurality ofregions formed by dividing the photoelectric image sensor, respectively;and an image synthesis unit for forming an image of the surface of theinspection object by synthesizing partial images outputted by thedetection signal transfer unit; the inspection device inspecting defectsor foreign matters of the surface of the inspection object by processingthe synthesized image; wherein the detection signal transfer unit has adetection signal correction function capable of bringing a detectionsignal from the photoelectric cell close to a reference target value ofa reference detection signal intensity determined for each of thechannels.

The detection system of the photoelectric sensor has light receptionelements (photoelectric cells) that are arranged eitherone-dimensionally or two-dimensionally and has channels (detectionsignal transfer unit) for transferring a detection signal to eachphotoelectric cell.

The detection signal transfer unit having a plurality of channels isconstituted in such a fashion as to be capable of individuallycorrecting the detection signals for each channel.

The inspection device according to the invention further includes anexternal input unit for sharing a correction target value (correctioncoefficient) as a correction target of the detection signal among aplurality of machines.

The invention can execute correction in such a fashion as to bring thedetection signal from each photoelectric cell close to the referencetarget value of the reference detection signal determined for eachchannel. Therefore, the invention can reduce the inspection sensitivitydifference resulting from variance of performance of constituentelements of a plurality of inspection devices and can achieve equivalentinspection sensitivity among a plurality of inspection devices(machines). The invention can further correct easily the change of thedetection signal owing to the change with time of the light source andthe cells and can conduct stable inspection.

The invention will be hereinafter described in further detail withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic construction of an inspection device accordingto an embodiment of the present invention;

FIG. 2 is a plan view of an illumination optical system 100 in theembodiment of the invention;

FIG. 3 is a schematic view of portions ranging from a detection system400 to an image processing system 500 in the embodiment of theinvention;

FIG. 4 is a flowchart of a correction coefficient calculation method inthe embodiment of the invention; and

FIGS. 5A to 5D show a management method of a target value in theembodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS Embodiment 1

An inspection device for inspecting a defect according to the inventionwill be explained with reference to FIG. 1.

The inspection device for inspecting a defect includes a stage 300 forsupporting thereon an inspection object 001 to be inspected and anillumination optical system 100 having a laser light source 101, a beamshaping unit 102 and a plurality of irradiation units 120, 121 and 122branched by an optical path branching/switching optical system.

This illumination optical system 100 irradiates a luminous flux of alight source (laser light source 101) to the test piece.

The inspection device for inspecting a defect further includes acondensation optical system 200 having an objective lens 201, a zoomlens group 202 and an imaging lens 203.

The condensation optical system 200 guides reflected and scattered lightreflected from the inspection object to a detection system to bedescribed later.

The inspection device for inspecting a defect further includes adetection system 400 having a light reception surface 401 which haslight reception devices arranged either one-dimensionally ortwo-dimensionally and which is divided into a plurality of regions, achannel group 501 for transferring a detection signal from the detectionsystem to each region and an image processing system 500 for processingthe detection signal 400 and executing defect judgment.

The channel group 501 operates as a detection signal transfer unit andhas a correction function of correcting the intensity of the detectionsignal as will be later described.

FIG. 2 is a plan view of the illumination optical system 100 forirradiating illumination light to the inspection object from threedirections.

A laser beam outgoing from the laser light source 101 is branched to twooptical paths by a branching optical device 110. One of the opticalpaths is reflected by mirrors 111 and 112 and is allowed to be incidentdownward to the beam shaping unit 102 by a mirror 113 to giveillumination light from a direction 11. The other travels towards abranching optical device 114 such as a half mirror.

One of the optical paths branched by the branching optical device 114 isreflected by a mirror 115 and is allowed to be incident downward to thebeam shaping unit 102 by a mirror 1137 to give an illumination beam froma direction 10. The other is allowed to be incident downward to the beamshaping unit 102 by a mirror 116 to give illumination light from adirection 12.

Incidentally, when illumination is made from only the direction 11,illumination can be achieved by switching from the branching opticaldevice 110 to a mirror device 118.

When illumination is made from two directions 10 and 12, illuminationcan be achieved by removing the optical branching device 110 from theoptical path or changing it to a pass-through optical device.

When illumination is made from only the direction 12 of the twodirections 10 and 12, for example, illumination can be achieved bychanging the branching optical device 114 to a mirror device 119.

FIG. 3 is a schematic view showing the flow of detection signals fromthe detection system 400 to the processing system 500.

The light reception surface 401 is constituted by light reception cellsthat are arranged either one-dimensionally or two-dimensionally and isdivided into regions 4011 to 4018.

Distribution 412 of the intensities of the detection signals of theregions 4011 to 4018 does not have a similar shape in a plurality ofdetection devices owing to variance of constituent elements such as theillumination system 100 and the condensation optical system 200.

The intensity 412 of the detection signal is corrected for each regionby each signal correction unit 5021 to 5028 provided individually toeach channel and the intensity distribution 512 of the detection signalafter correction can be changed to an arbitrary shape by thiscorrection.

Here, the correction units 5021 to 5028 are constituted in such afashion as to acquire a simple proportional gain.

A correction coefficient storage unit 505 stores a correctioncoefficient that is different depending on each optical condition andthis correction coefficient is set to each correction unit 5021 to 5028in accordance with the optical condition. In consequence, correction canbe made while the change of the optical characteristics in the casewhere the illumination direction and a magnification ratio are changedis taken into consideration.

The detection signal so corrected is digitized by A/D converters 5031 to5038 and is imaged by image formation units 5061 to 5068. The images arecombined by an image synthesis unit 507 and are transferred to an imageprocessing unit 504.

The image processing unit 504 executes a comparison processing of theimages aligned in a scanning direction and inspects an image defect ofthe inspection object and adhering dust.

Correction by the correction unit described above is brought forth bythe correction coefficient shown in FIG. 3. Explanation will be furthergiven on this correction coefficient.

The detection signal of a photo-electric image sensor has a distribution412 of the output intensity as shown in FIG. 3. The distribution 412 ofthis output intensity is corrected so as to attain an intensitydistribution 512 (distribution having a shape like a curve of the secondorder describing maximum at the center and minimum at both ends withrespect to the arrangement direction of eight photoelectric cells) aftercorrection.

A reference target value of reference signal intensity is inputted byexternal input means 530 to the target value storage unit 550.

Reference target values QA(1) to QA(8) are allocated to an A column insuch a fashion as to correspond to the arrangement of the eightphotoelectric cells (channels CH1 to CH8) and the optical conditions (A,B, C and D). The reference target values are likewise allocated inaccordance with other conditions B to D, respectively.

The reference target values of the reference signal intensity have adistribution of a shape analogous to a curve of the second order inwhich the maximum value exists at the center and the minimum value, atboth ends.

The correction coefficient calculation unit 520 calculates a correctioncoefficient. The correction coefficient so calculated is stored in thecorrection coefficient storage unit 505. Correction coefficients CA(1)to CA(8) are allocated to the A column in such a fashion as tocorrespond to the arrangement of the eight photoelectric cells (channelsCH1 to CH8) and the optical conditions (A, B, C and D) in the correctioncoefficient storage unit 505. The correction coefficients are likewiseallocated in accordance with other conditions B to D, respectively.

FIG. 4 is a flowchart showing a correction method according to theembodiment of the invention. This flowchart shows the correction methodfor keeping performance matching of the inspection sensitivity of eachinspection device. The correction coefficient is decided in accordancewith the flow shown in FIG. 4 for each optical condition.

Explanation will be given first on the case where correction is made asfor the condition A. In step S1 (test wafer inspection procedure 1), aninspection object as a reference (test wafer, in this case) 001 isinspected and the output intensity of the detection image signal foreach channel is acquired.

The test wafer hereby used is the one that is prepared by applying PSL(polystyrene latex) to a part or the entire surface of a bare wafer.Alternatively, the test wafer may be a wafer having a uniform reflectionfactor on its entire surface.

At this time, scattered light from the test wafer 001 for each region isreceived and the sum of the output for each pixel outputted is definedas the intensity of the detection signal in the region. Alternatively,the sum of luminance inside a search area of each region of the imageacquired by the inspection may be defined as the intensity of thedetection signal.

The intensity of the detection signal so obtained is expressed as PA1[i](i: sensor region number).

In this instance, the correction unit 502 does not correct the detectionsignal and the detection signal obtained itself by the detection system400 is transferred to the image processing unit 504.

In step S1 (test wafer inspection procedure 1), the intensity QA[i] ofthe detection signal as the target for each channel, corresponding tothe set optical condition, is acquired from the correction coefficientstorage unit 505 and the correction coefficient calculation unit 530calculates the correction function that renders the intensity PA1[i] ofthe detection signal acquired in step S1 (test wafer inspectionprocedure 1) coincident with the intensity QA[i] of the target detectionsignal.

Here, a simple proportion is used as the correction function. That is,CA[i] is used as a coefficient and is set to CA[i]=PA1[i]/AQ[i]. Thevalue CA[i] calculated in this manner is stored in the correctioncoefficient storage unit 505.

In step S3 (test wafer inspection procedure 3), the correctioncoefficient CA[i] of the corresponding optical condition (here, opticalcondition A) is called out from the correction coefficient storage unit505 and is set to each of the correction units 5021 to 5028.

The test wafer is inspected under this condition and the intensity ofthe detection signal is acquired. The intensity PA2[i] of the detectionsignal corrected and the target value QA[i] are compared and correctionis finished when the difference of the intensities of the detectionimage signals of each channel remains within the allowable range.

When the difference exceeding the allowable range exists, the flowproceeds to step S4 (optical system re-adjustment procedure) andreadjustment of the optical system such as re-examination of parametersunder that optical condition is carried out. The flow then returns againto step S1 and a series of flows is executed.

Incidentally, T1 is a target coincidence judgment branch.

FIGS. 5A to 5D show several examples of the correction target value whencorrection of the inspection sensitivity of the inspection device iscarried out.

The intensity QA[i] of the detection signal on the output side as thetarget intensity of the detection signal of each channel may well be anarbitrary function by taking into account an illumination intensitydistribution depending on the illumination optical system and thedetection optical system.

When laser is used as the light source, for example, the intensity maybe a secondary function QA[i]=a(i−c)²+b (a, b and c: real numbers) or aregular distribution when the influences of the intensity distributionand aberration of the lenses of the illumination optical system arecollectively taken into account.

Alternatively, it is possible to select a master from among a pluralityof applicants and (when correction is carried out under the opticalcondition A) to set MA[i] of the actual detection signal on the outputside to the intensity B[i] of the detection signal as the target. Stillalternatively, NA[i] obtained by approximating this detection signalMA[i] on the output side by an arbitrary function may be used.

FIGS. 5A to 5D illustrate means for sharing the intensity value QA[i] ofthe detection signal as the target among a plurality of devices. Theintensity QA[i] of the detection signal as the target may beindividually acquired by external input means 530 provided to anindividual inspection device 601 as shown in FIG. 5A.

Alternatively, it is possible to connect a plurality of inspectiondevices to a high order management apparatus 611, to store the intensityB[i] of the detection signal as the target in the high order managementapparatus 611 and to transfer the intensity B[i] to the individualinspection device when the correction coefficient is calculated.

Still alternatively, the following construction can be employed. Namely,the high order management apparatus 611 has therein a correctioncoefficient calculation unit 530 and a correction target value storageunit 505. When the correction coefficient is calculated, PA1[i] andPA2[i] of the detection signals on the output side of the individualinspection devices 601 are transferred and calculation of the correctioncoefficient is executed inside the high order management apparatus 611.The correction coefficient so calculated is transferred to theindividual inspection device 601 and is stored in the correctioncoefficient storage unit 505.

The high order management apparatus may be installed inside the sameplant or at a remote place while connected through a network such as theInternet. The number of the high order management apparatus may beeither plural or single.

The correction target value QA[i] may be only one kind. Alternatively,different target values may be set at different production sites and maybe unified only inside the same place or within a predetermined range.

Still alternatively, the correction target value QA[i] may be acquiredby setting a master machine 621 from among a plurality of devices asshown in FIG. 5C and may be used as the intensity of the detectionsignal when the inspection object as the reference is inspected.

The master machine 621 may be connected through a network such as theInternet as shown in FIG. 5D.

It should be further understood by those skilled in the art thatalthough the foregoing description has been made on embodiments of theinvention, the invention is not limited thereto and various changes andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

1. An inspection device for inspecting defects or foreign matters on asurface of an inspection object, comprising: a light source forirradiating a luminous flux to said inspection object; an optical systemfor guiding reflected and scattered light reflected from said inspectionobject; a photoelectric image sensor having a plurality of photoelectriccells arranged, for converting said reflected and scattered light guidedto electric detection signals; a detection signal transfer unit havingchannels each constituted by a signal correction unit, an A/D converterand an image formation unit, and corresponding to each of a plurality ofregions formed by dividing said photoelectric image sensor,respectively; and an image synthesis unit for forming an image of thesurface of said inspection object by synthesizing partial imagesoutputted by said detection signal transfer unit; said inspection deviceinspecting defects or foreign matters of the surface of said inspectionobject by processing said synthesized image; wherein said detectionsignal transfer unit has a detection signal correction function capableof bringing a detection signal from said photoelectric cell close to areference target value of a reference detection signal intensitydetermined for each of said channels.
 2. An inspection device accordingto claim 1, which further comprises an external input unit for acquiringthe reference target value of said reference detection signal intensityfrom outside.
 3. An inspection device according to claim 2, wherein saidphotoelectric cells are arranged either one-dimensionally ortwo-dimensionally on coordinates in said photoelectric image sensor. 4.An inspection device according to claim 2, which further comprises: acorrection coefficient calculation unit for comparing an intensity ofthe detection signal acquired by inspection of said reference inspectionobject with an intensity of said reference detection signal andcalculating a correction coefficient for bringing the detection signalclose to said reference target value, and a correction coefficientstorage unit for storing said correction coefficient; wherein saidcorrection coefficient of said correction coefficient storage unit isprovided to said signal correction function.
 5. An inspection deviceaccording to claim 4, wherein said correction coefficient calculationunit calculates said correction coefficient for each channel, and saidcorrection coefficient for each channel is stored in said correctioncoefficient storage unit.
 6. An inspection device according to claim 1,wherein correction by said detection signal correction function iscarried out under a plurality of optical conditions of said opticalsystem.
 7. An inspection device according to claim 4, whereincalculation of said correction coefficient is made either periodicallyor non-periodically by said correction coefficient calculation unit. 8.An inspection system comprising a plurality of inspection devices, eachof said inspection devices including: a light source for irradiating aluminous flux to an inspection object; an optical system for guidingreflected and scattered light reflected from said inspection object; aphotoelectric image sensor having a plurality of photoelectric cellsarranged, for converting said reflected and scattered light guided toelectric detection signals; a detection signal transfer unit havingchannels each constituted by a signal correction unit, an A/D converterand an image formation unit, and corresponding to each of a plurality ofregions formed by dividing said photoelectric image sensor; and an imagesynthesis unit for forming an image of the surface of said inspectionobject by synthesizing partial images outputted by said detection signaltransfer unit; said inspection devices inspecting defects or foreignmatters of the surface of said inspection object by processing saidsynthesized image; wherein said inspection system includes a managementunit for managing said inspection devices.
 9. An inspection systemaccording to claim 8, which further comprises: a correction coefficientcalculation unit for comparing an intensity of the detection signalacquired by inspection of said reference inspection object with anintensity of said reference detection signal and calculating acorrection coefficient for bringing the detection signal close to saidreference target value, and a correction coefficient storage unit forstoring said correction coefficient; wherein said correction coefficientof said correction coefficient storage unit is provided to said signalcorrection function.
 10. An inspection system according to claim 9,wherein said correction coefficient calculation unit and said correctioncoefficient storage unit are provided to said management unit.
 11. Aninspection method for an inspection device for inspecting defects orforeign matters on a surface of an inspection object, said inspectiondevice including: a light source for irradiating a luminous flux to aninspection object; an optical system for guiding reflected and scatteredlight reflected from said inspection object; a photoelectric imagesensor having a plurality of photoelectric cells arranged, forconverting said reflected and scattered light guided to electricdetection signals; a detection signal transfer unit having channels eachconstituted by a signal correction unit, an A/D converter and an imageformation unit, and corresponding to each of a plurality of regionsformed by dividing said photoelectric image sensor; and an imagesynthesis unit for forming an image of the surface of said inspectionobject by synthesizing partial images outputted by said detection signaltransfer unit; said inspection device inspecting defects or foreignmatters of the surface of said inspection object by processing saidsynthesized image; wherein said detection signal transfer unit iscorrected in such a fashion as to bring the detection signal from saidphotoelectric cell close to a reference target value of a referencedetection signal intensity determined for each channel.
 12. Aninspection method according to claim 11, wherein the reference targetvalue of said reference detection signal intensity is acquired fromoutside.
 13. An inspection method according to claim 12, wherein aninspection device further includes a correction coefficient calculationunit for comparing an intensity of the detection signal acquired byinspection of said reference inspection object with an intensity of saidreference detection signal and calculating a correction coefficient forbringing the detection signal close to said reference target value, anda correction coefficient storage unit for storing said correctioncoefficient, and said correction coefficient of said correctioncoefficient storage unit is provided to said signal correction function.14. An inspection method according to claim 13, wherein said correctioncoefficient calculation unit calculates said correction coefficient foreach channel, and said correction coefficient for each channel is storedin said correction coefficient storage unit.
 15. An inspection methodaccording to claim 14, wherein correction by said detection signalcorrection function is carried out under each of a plurality of opticalconditions of said optical system.
 16. An inspection method according toclaim 13, wherein calculation of the correction coefficient is madeeither periodically or non-periodically by said correction coefficientcalculation unit.
 17. An inspection method according to claim 11, whichcan execute a transmission processing of transmitting the referencetarget value of said detection signal intensity and a detection signalobtained by the inspection of a reference inspection object as areference target value to other inspection devices.
 18. An inspectiondevice according to claim 1, wherein said reference target value of saidreference detection signal intensity has a distribution like a curve ofthe second order which attains a maximum value at a center of a channeland a minimum value at both ends.
 19. An inspection device according toclaim 1, wherein each of said channels of said detection signal transferunit has a correction unit, an A/D converter and an image formationdevice arranged in the order named from the input side of the detectionsignal, and the detection signal is corrected by gain adjustment of saidcorrection unit bearing said detection image signal correction function.